Embodiments of the inventive concepts relate to a positive active material for a rechargeable sodium battery and a method of fabricating the same. More particularly, embodiments of the inventive concepts relate to a positive active material for a rechargeable sodium battery and a method of fabricating the same, in which a kind of a sodium source is changed depending on a content of nickel or manganese included in a metal hydroxide precursor.
Rechargeable batteries capable of storing electrical energy have been increasingly demanded with the development of portable mobile electronic devices (e.g., smart phones, MP3 players, and tablet personal computers) and electric cars.
A lithium metal oxide may be used as a positive active material in a lithium ion rechargeable battery among the rechargeable batteries. In particular, LiCoO2, LiMn2O4, or LiNiO2 may be used as the lithium metal oxide. A cobalt-based lithium oxide among these materials has been commercialized and widely used. However, cobalt is expensive and harmful. A nickel-based lithium oxide is inexpensive and less harmful and realizes high capacity of a lithium ion rechargeable battery. However, powder synthesis of the nickel-based lithium oxide may not be easy and life characteristics of the nickel-based lithium oxide may be poor. A lithium composite oxide represented as LiMM′Ox has been developed to solve these problems. Here, “M” and “M′” are transition metals such as Co, Mn, Ni, V, Fe, and/or W. In other words, a portion of Ni in LiNiO2 is substituted with another metal to form the lithium composite oxide, and thus the synthesis of the lithium composite oxide may be easier and life characteristics of the lithium composite oxide may be improved. The improvement of these characteristics may be affected by a crystal structure or a particle shape of lithium oxide finally formed. For example, Korean Patent Publication No. 10-1999-0034749 (Application No. 10-1997-0056445, Applicant: Samsung SDI Co., Ltd.) discloses a lithium secondary battery that employs a lithium composite oxide (LiNi(1-x-y)CoxMyO2, where “M” is at least one metal atom selected from a group consisting of Al, Ca, Mg, and B, “x” ranges from 0.1 to 0.3, and “y” ranges from 0 to 0.1) to realize excellent capacity, excellent reversibility, and stable periodic life thereof. Here, the lithium composite oxide is used as a positive electrode material for the lithium secondary battery.